Under the guidance of former archbishop Hélder Câmara, who has died aged 90 in Recife, the Catholic church in Brazil became an outspoken critic of the 1964-85 military dictatorship and a powerful movement for social change.

Câmara, once nominated for the Nobel Peace Prize, was an early proponent of "liberation theology", a belief that the the poor should not have to wait until the afterlife to free themselves from misery. Liberation theology politicised the church's charitable work and brought criticisms that it was encouraging the armed revolutionary struggles that swept Latin America during the 1970s and 1980s. Câmara was called by his opponents "the Red Bishop" and "Fidel Castro in a cassock".

He once answered his detractors: "When I fed the poor, they called me a saint. When I asked, 'Why are they poor?' they called me a communist." With other clerics, he encouraged peasants to think beyond their conventionally fatalistic outlook by studying the gospels in small groups and asking what conclusions could be drawn for social change.

Câmara worked in the favela shanty towns of Rio, and was made archbishop of Olinda and Recife in the north-east of Brazil - impoverished through both drought and antiquated systems of land tenure - where he saw at first hand the social inequalities that result from Brazil having one of the most unfair distributions of wealth in the world. He helped push for a radical transition for the church in Brazil - the world's most populous Catholic nation - from being an ally of the establishment to a defender of the poor and a relentless campaigner for education and agrarian reform.

The north-east was where Câmara was born, in the city of Fortaleza. He was one of 13 children, and is said to have declared at the age of four that he wanted to become a priest. He entered a seminary at 14, and was ordained at 22.

Soon he became an active member of the Integralist movement, a Brazilian outgrowth of fascism, at which point he expressed strong anti-communist views. He left it after several years, describing the episode as an act of youthful folly. Thereafter he was wary of direct involvement in politics, preferring to work with trade unions and lay catholic movements, always aware that just causes could be hijacked by extremist guerillas or government supporters.

Câmara rose through the church's ranks to become auxiliary bishop of Rio de Janeiro in 1952, the year in which he founded the National Conference of Brazilian Bishops (CNBB), with the permission of Vatican official Giovanni Battista Montini, a valuable contact who went on to become Pope Paul VI. Serving as secretary-general of the CNBB for 12 years, Câmara was in regular contact with Brazil's political bureaucracy and three presidents.

When the Second Vatican Council was meeting in Rome in 1963, Câmara called on his fellow bishops to drop such titles as "excellency" and "eminence", and to exchange their silver and gold pectoral crosses for bronze or wooden ones. "Let us end once and for all the impression of a bishop-prince, residing in a palace, isolated from his clergy whom he treats distantly and coldly," he wrote in a paper to the bishops.

When he arrived in Recife as archbishop in 1964, he put the archbishop's traditional gilded throne in storage and replaced it with a simple wooden chair. He chose not to live in the palatial official residence. Instead, he lived in a sparsely furnished room behind a church.

Twenty days after he arrived at the archdiocese, Brazil's military seized power. When the regime began a campaign of repression, many church lay leaders and clerics were among the victims. Câmara travelled abroad, denouncing the torture and killing of priests, nuns and seminary students. His phone was tapped, he received death threats by phone and mail and, in 1969, a hail of bullets pierced the walls of his living quarters, though he was out of the country at the time.

In May 1970, at a conference in Paris, he spoke out about the torture and was subsequently banned from giving talks or interviews in Brazil. He became an international hero of the Catholic left and was nominated for a Nobel Peace Prize. A biography later revealed that his country's military leaders had campaigned against his being awarded the prize.

In 1980, Pope John Paul II went to Recife and met Câmara, then considered a "non-person" by the military government. On live television - broadcast nationally and internationally - the Pope embraced him and said: "This man is a friend of the poor. He is my friend."

Câmara retired as archbishop in 1985, but continued to criticise the role of multinational corporations and industrialised nations in the third world.

Brazilian President Fernando Henrique Cardoso declared three days of national mourning in Câmara's honour, and the Argentine philosopher and theologian Enrique Dussel said of him: "He was short in height, but huge in stature when he spoke to the crowds. He was one of the first to criticise the dictatorship... and he dedicated his life, along with other bishops... to the poor in Latin America."

Jan Rocha writes: In April 1969, my husband Plauto and I went to hear Hélder Câmara speak at a third world conference at the Roundhouse in London. An outspoken critic of the military dictatorship, he was banned from speaking in Brazil.

At the Roundhouse, with the vigorous voice that belied his tiny figure, he said that the real violence was the poverty of the people, not those who took up arms against their oppressors.

A friend had suggested that we ask him to baptise our baby son Camilo, named after the revolutionary Colombian priest Camilo Torres. He agreed immediately, as long as we would take him to the airport to catch his plane back to Brazil afterwards. We squeezed the archbishop into a friend's small car and drove hell for leather to the Catholic church in Kew. Summoned by a hasty phone call, the local priest appeared and knelt before the unlikely archbishop - in his worn black cassock - to kiss his ring.

Halfway through the baptism, Vamberto Morais, head of the BBC's Brazilian Service and his wife Lourdes, who were fervent admirers of the archbishop and had heard about the ceremony, arrived bearing a wobbly pudim (Brazilian blancmange) for the hurried baptismal tea in our flat round the corner.

We did not have a car, so we took the archbishop to Gatwick by tube and train. He did not turn a hair, but chatted about his friend the Pope, Paul VI. At the airport he asked us to leave him so that he could be alone to pray.

This was what made Hélder Câmara loved by ordinary people and hated by dictators and torturers - his extreme humility, his extreme humanity.

Back home we discovered that two priests had appeared hotfoot at the door, eager to invite the famous "red" archbishop to dinner.